Sheet conveying device, image forming apparatus, and method of detecting double-feed of sheet

ABSTRACT

According to an embodiment, a sheet conveying device includes: a first roller configured to correct a tilt of a sheet to be conveyed; a first detecting unit located further on an upstream side in a conveying direction of the sheet than the first roller and configured to detect information concerning double-feed of the sheet; a second roller configured to convey the sheet to the first roller; a driving unit configured to drive the second roller; and a controller configured to control the driving unit to thereby temporarily stop the conveyance of the sheet in order to perform the detection by the first detecting unit in a state in which an end of the sheet on a downstream side in the conveying direction of the sheet is located further on the upstream side in the conveying direction of the sheet than a nip position of the first roller.

CROSS-REFERENCE TO RELATED APPLICATION

This application is also based upon and claims the benefit of priorityfrom U.S. provisional application 61/248910, filed on Oct. 6, 2009; theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a technique forperforming double-feed detection for a sheet.

BACKGROUND

In the past, double-feed detection for an original document conveyed inan auto document feeder is performed in a state in which the originaldocument is bent by bringing the original document into contact with analigning roller that corrects a tilt of the original document.

However, since a positional relation between a sensor that performs thedouble-feed detection and the original document is unstable, stabledouble-feed detection cannot be performed.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an image forming apparatus;

FIG. 2 is a sectional view of an auto document feeder;

FIG. 3 is a block diagram of components related to document conveyanceby the auto document feeder;

FIG. 4 is a flowchart for explaining the operation of the auto documentfeeder;

FIG. 5 is a sectional view of the auto document feeder, wherein anoriginal document located in a double-feed detection position isschematically shown; and

FIG. 6 is a sectional view of the auto document feeder, wherein aposition of the original document at the time when a motor driving unitstops is schematically shown.

DETAILED DESCRIPTION

In general, according to an embodiment, a sheet conveying deviceincludes: a first roller configured to correct a tilt of a sheet to beconveyed; a first detecting unit located further on an upstream side ina conveying direction of the sheet than the first roller and configuredto detect information concerning double-feed of the sheet; a secondroller configured to convey the sheet to the first roller; a drivingunit configured to drive the second roller; and a controller configuredto control the driving unit to thereby temporarily stop the conveyanceof the sheet in order to perform the detection by the first detectingunit in a state in which an end of the sheet on a downstream side in theconveying direction of the sheet is located further on the upstream sidein the conveying direction of the sheet than a nip position of the firstroller.

FIG. 1 is a sectional view of an image forming apparatus. An imageforming apparatus 1 may be a MFP (Multi Function Printer).

Referring to FIG. 1, the image forming apparatus 1 includes an imagereading unit R and an image forming unit P. The image reading unit Rscans and reads images of a sheet document and a book document.

The image forming unit P forms a developer image on a sheet on the basisof an image read from an original document by the image reading unit Ror print data transmitted to the image forming apparatus 1 by anexternal apparatus.

The image reading unit R includes an auto document feeder (ADF) 9configured to automatically convey an original document to apredetermined image reading position. The image reading unit R reads,with a scanning optical system 10, an image of an original documentautomatically conveyed by the auto document feeder 9 and placed on adocument tray (a predetermined document placing table) Rt or an originaldocument placed on a not-shown document table.

The image forming unit P includes toner cartridges 1Y to 1K,photoconductive members 2Y to 2K, developing rollers 3Y to 3K, mixers 4Yto 4K, an intermediate transfer belt 6, a fixing device 7, and adischarge tray 8.

The image forming apparatus 1 according to this embodiment includes acontroller 801, a memory 803, an operation display unit 805, and acommunication unit 807.

The controller 801 has a role of performing various kinds of processingin the image forming apparatus 1 and also has a role of realizingvarious functions by executing computer programs stored in the memory803. The memory 803 may be, for example, a RAM (Random Access Memory), aROM (Read Only Memory), a DRAM (Dynamic Random Access Memory), an SRAM(Static Random Access Memory), or a VRAM (Video RAM). The memory 803 hasa role of storing various kinds of information and computer programsused in the image forming apparatus 1.

Various kinds of setting are displayed on the operation display unit805. The operation display unit 805 may be an LCD (Liquid CrystalDisplay), an EL (Electronic Luminescence), a PDP (Plasma Display Panel),or a CRT (Cathode Ray Tube).

The various kinds of setting are changed by operating the operationdisplay unit 805. The operation display unit 805 may be a touch paneltype.

An overview of copying is explained below as an example of processing inthe image forming apparatus according to this embodiment.

First, sheets picked up from cassettes enter a sheet conveying path. Thesheets entered the sheet conveying path are moved in a predeterminedconveying direction by plural roller pairs.

Images of plural sheet documents continuously automatically conveyed bythe auto document feeder 9 are read by the scanning optical system 10 inthe predetermined image reading position.

On the basis of print data of the images read from the originaldocuments by the image reading unit R, electrostatic latent images areformed on photoconductive surfaces of the photoconductive members 2Y,2M, 2C, and 2K for transferring developer images of yellow (Y), magenta(M), cyan(C), and black (K) onto the sheets.

Subsequently, developers agitated by the mixers 4Y to 4K in a developingdevice are deposited by the developing rollers 3Y to 3K on thephotoconductive members 2Y to 2K on which the electrostatic latentimages are formed as explained above. Consequently, the electrostaticlatent images formed on the photoconductive surfaces of thephotoconductive members are visualized.

Developer images formed on the photoconductive members in this way aretransferred onto a belt surface of the intermediate transfer belt 6(so-called primary transfer). The developer images conveyed by therotation of the intermediate transfer belt 6 are transferred onto theconveyed sheets in a predetermined secondary transfer position T.

The developer images transferred onto the sheets are heated and fixed onthe sheets by the fixing device 7. The sheets having the developerimages heated and fixed thereon are conveyed in the conveying path byplural conveying roller pairs and sequentially discharged onto thedischarge tray 8.

The auto document feeder 9 is explained below. FIG. 2 is an enlargedsectional view of the auto document feeder. An original document is seton a document tray 11. The document may be plural documents or onedocument.

A pickup roller 12 as a third roller picks up the original documentlocated on the document tray 11 and conveys the original document to apaper feeding roller 13 as a second roller. The paper feeding roller 13conveys the original document picked up by the pickup roller 12 todownstream in the conveying direction. Rotating shaft sections of thepickup roller 12 and the paper feeding roller 13 are connected to eachother via a transmission mechanism 18. The transmission mechanism 18 maybe a belt or a pulley.

FIG. 3 is a block diagram of components related to document conveyanceby the auto document feeder 9. Referring to the figure, the pickuproller 12 moves up and down according to the operation of a solenoiddriving unit 40. The solenoid driving unit 40 includes a solenoid driver41 and a pickup solenoid 42.

Referring to FIG. 2, a separation roller 14 as a fourth roller islocated to be opposed to the paper feeding roller 13. When the pickuproller 12 picks up two or more original documents, a load of a torquelimiter of the separation roller 14 is increased by frictional force ofthe original documents and the separation roller 14 stops. The stoppedseparation roller 14 comes into contact with the original document onthe lower side to thereby suppress the original document on the lowerside from being conveyed further down stream.

An aligning roller 15 as a first roller comes into contact with theoriginal document conveyed by the paper feeding roller 13 to correct atilt of the original document. The aligning roller 15 includes tworoller set in contact with each other. The aligning roller 15 brings theoriginal document into contact with a nip section where the rollers arein contact with each other to be bent to thereby correct the tilt of theoriginal document.

Referring to FIG. 3, a motor driving unit 30 drives the pickup roller12, the paper feeding roller 13, and the aligning roller 15. The motordriving unit 30 includes a motor driver 31 and a document feeding motor32.

The document feeding motor 32 may be a stepping motor. The controller801 outputs a pulse signal to the motor driver 31. The motor driver 31supplies driving current to the document feeding motor 32 on the basisof the received pulse signal.

The controller 801 controls the number of pulses of the pulse signaloutput to the motor driver 31 to thereby control an amount of driving ofthe document feeding motor 32.

The document feeding motor 32 normally rotates, whereby the pickuproller 12 and the paper feeding roller 13 rotate. The document feedingmotor 32 reversely rotates, whereby the aligning roller 15 rotates.

An aligning sensor 16 is located between the separation roller 14 andthe aligning roller 15. The aligning sensor 16 detects arrival of theoriginal document conveyed by the separation roller 14.

A double-feed detecting unit 17 is located between the aligning roller15 and the aligning sensor 16. The double-feed detecting unit 17 may bea non-contact sensor. The non-contact sensor may be an ultrasonicsensor.

When the double-feed detecting unit 17 is the ultrasonic sensor, thedouble-feed detecting unit 17 includes an ultrasound generating unit 17a and an ultrasound receiving unit 17 b. The ultrasound generating unit17 a and the ultrasound receiving unit 17 b are opposed to each otheracross the conveying path for the original document. The ultrasoundgenerating unit 17 a is located further on a downstream side in theconveying direction of the original document than the ultrasoundreceiving unit 17 b. The ultrasound generating unit 17 a and theultrasound receiving unit 17 b may be obliquely opposed to each otherwith respect to the conveying path for the original document. Since theultrasound sound generating unit 17 a and the ultrasound receiving unit17 b are obliquely opposed to each other, detection accuracy isimproved.

The ultrasound receiving unit 17 b receives ultrasound output by theultrasound generating unit 17 a. The ultrasound penetrated into theoriginal document is attenuated. When the number of original documentsincreases, a degree of the attenuation increases. The ultrasoundreceiving unit 17 b outputs a signal corresponding to the intensity ofthe received ultrasound to the controller 801.

When original documents entered a position for detection by thedouble-feed detecting unit 17 are superimposed, the intensity of theultrasound received by the ultrasound receiving unit 17 b is smallerthan that of the ultrasound received in a normal case, i.e., when oneoriginal document is detected. The controller 801 discriminates,according to the intensity of the signal output from the ultrasoundreceiving unit 17 b, whether the original documents are double-fed.

The controller 801 controls driving timing for the aligning roller 15such that the original document coming into contact with the aligningroller 15 to be bent is conveyed to be timed to coincide with a tonerimage formed on the intermediate transfer belt 6.

The operation of the auto document feeder 9 is explained with referenceto a flowchart of FIG. 4. In Act 101, the controller 801 controls thesolenoid driving unit 40 to thereby move down the pickup roller 12toward a pickup position for picking up an original document placed onthe document tray 11.

In Act 102, the controller 801 controls the motor driving unit 30 tothereby drive the pickup roller 12 and the paper feeding roller 13. Theoriginal document picked up by the pickup roller 12 moves downstream. InAct 103, the controller 801 determines whether the aligning sensor 16detects the original document.

If the aligning sensor 16 detects the original document, the controller801 proceeds to Act 104. In Act 104, the controller 801 starts countingof the number of pulses output to the motor driver 31.

In Act 105, the controller 801 determines whether the counted number ofpulses reaches N1. If the number of pulses reaches N1, the controller801 proceeds to Act 106.

The controller 801 stops the driving of the motor driving unit 30 andstops the conveyance of the original document. A position where theconveyance of the original document is stopped is a double-feeddetection position where double-feed detection is performed by thedouble-feed detecting unit 17.

N1 is set such that an end of the original document on the downstreamside in the conveying direction of the original document is locatedfurther on an upstream side in the conveying direction than the nipsection of the aligning roller 15. FIG. 5 is a sectional view of theauto document feeder, wherein the original document located in thedouble-feed detection position is schematically shown. Referring to thefigure, the original document stops before coming into contact with thealigning roller 15 and is located along the conveying path without beingbent.

Even if a slip occurs when the original document is conveyed by thepickup roller 12 and the paper feeding roller 13, the slip does notaffect the stop control for the original document. Specifically, thestop control for the original document is performed by using a detectionresult of the aligning sensor 16 located between the paper feedingroller 13 and the aligning roller 15. Therefore, fluctuation in thedouble-feed detection position is suppressed.

In Act 107, the controller 801 determines, on the basis of a signaloutput by the ultrasound receiving unit 17 b, whether the originaldocuments are double-fed. Since the original document is located flatalong the conveying path without being bent, accuracy of double-feeddetection is improved.

If the original documents are double-fed, in Act 108, the controller 801displays indication of the double-feed on the operation display unit805. If the original documents are not double-fed, the controller 801proceeds to Act 109.

In Act 109, the controller 801 drives the motor driving unit 30 againand rotates the paper feeding roller 13. In Act 110, the controller 801starts counting of the number of pulses output to the motor driver 31.

In Act 111, the controller 801 determines whether the counted number ofpulses reaches N2. If the number of pulses reaches N2, the controller801 proceeds to Act 112 and stops the driving of the motor driving unit30.

FIG. 6 is a sectional view of the auto document feeder 9, wherein theposition of the original document at the time when the motor drivingunit 30 stops is schematically shown. Referring to the figure, theoriginal document is bent because the original document is preventedfrom being conveyed downstream by coming into contact with the aligningroller 15.

In Act 113, the controller 801 discriminates whether scanning timing isreached. The scanning timing means timing when the original document islocated in the image reading position at the start of scanning by thescanning optical system 10.

In Act 114, the controller 801 controls the motor driving unit 30 tothereby reversely rotate the driving of the document feeding motor 32and rotate the aligning roller 15. The original document is nipped bythe aligning roller 15 and moves to the image reading position. Aconveying operation performed until the original document reaches fromthe aligning roller 15 to the image reading position is omitted.

First Modification

As a method of stopping an original document in the double-feeddetection position, the controller 801 counts the number of pulsesoutput to the motor driver 31 after the detection by the aligning sensor16. However, the controller 801 may count driving time of the paperfeeding roller 13. Specifically, the controller 801 may measure time inwhich the paper feeding roller 13 performs the rotation operation andstop the motor driving unit 30 when the measured time reaches apredetermined time. It is also possible that the predetermined time iscalculated from rotating speed of the paper feeding roller 13, thecalculated predetermined time is stored in the memory 803, and thecontroller 801 reads out information concerning the predetermined timefrom the memory 803 and performs the control.

Second Modification

The double-feed detecting unit 17 may be another non-contact sensor. Theother non-contact sensor may be an optical sensor. The optical sensorincludes a light emitting element and a light receiving element. Thelight emitting element and the light receiving element are locatedacross an original document. The controller 801 discriminates presenceor absence of double-feed from a light amount of light received by thelight receiving element.

Third Modification

The document feeding motor 32 may be a DC motor. The DC motor includes aphotointerrupter in an output shaft. The controller 801 controls adriving amount of the DC motor according to the number of times thephotointerrupter interrupts light.

Fourth Modification

In the embodiment, the auto document feeder 9 configured to convey anoriginal document to the image reading position is explained. However,the embodiment can also be applied to a conveying system for a sheet fedfrom a cassette tray or a manual feed tray. Specifically, it is alsopossible to temporarily stop conveyance of the sheet in a positionfurther on the upstream side in the conveying direction than an aligningroller included in the conveying system for the sheet fed from thecassette tray or the manual feed tray and perform the double-feeddetection.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of invention. Indeed, the novel apparatus and methods describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the apparatus andmethods described herein may be made without departing from the sprit ofthe inventions. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the inventions.

1. A sheet conveying device comprising: a first roller configured tocorrect a tilt of a sheet to be conveyed; a first detecting unit locatedfurther on an upstream side in a conveying direction of the sheet thanthe first roller and configured to detect information concerningdouble-feed of the sheet; a second roller configured to convey the sheetto the first roller; a driving unit configured to drive the secondroller; and a controller configured to control the driving unit tothereby temporarily stop the conveyance of the sheet in order to performthe detection by the first detecting unit in a state in which an end ofthe sheet on a downstream side in the conveying direction of the sheetis located further on the upstream side in the conveying direction ofthe sheet than a nip position of the first roller.
 2. The deviceaccording to claim 1, further comprising a second detecting unit locatedbetween the second roller and the first detecting unit and configured todetect entrance of the sheet, wherein the controller starts, when thesecond detecting unit detects the entrance of the sheet, control forstopping the sheet in a position of the detection by the first detectingunit.
 3. The device according to claim 2, wherein the driving unitincludes: a pulse motor; and a driver for the pulse motor, and thecontroller stars, when the second detecting unit detects the entrance ofthe sheet, counting of a number of pulses output to the driver and stopsthe sheet in the position of the detection by the first detecting uniton the basis of a result of the counting.
 4. The device according toclaim 1, wherein the first detecting unit is a non-contact detectingunit.
 5. The device according to claim 4, wherein the first detectingunit includes: an ultrasound generating unit configured to generateultrasound; and an ultrasound receiving unit configured to receive theultrasound generated by the ultrasound generating unit, and theultrasound generating unit and the ultrasound receiving unit are opposedto each other across a conveying path for the sheet.
 6. The deviceaccording to claim 5, wherein the ultrasound generating unit is locatedfurther downstream in the conveying direction of the sheet than theultrasound receiving unit.
 7. The device according to claim 2, whereinthe second detecting unit is located below a conveying path for thesheet .
 8. The device according to claim 1, further comprising a thirdroller configured to pick up the sheet to the second roller, wherein thesecond and third rollers are connected by a transmission mechanism. 9.The device according to claim 8, wherein the second roller is opposed toa fourth roller, the fourth roller inhibits double-feed of the sheetpicked up by the third roller.
 10. An image forming apparatuscomprising: a document conveying unit including: a first rollerconfigured to correct a tilt of an original document to be conveyed; afirst detecting unit located further on an upstream side in a conveyingdirection of the original document than the first roller and configuredto detect information concerning double-feed of the original document; asecond roller configured to convey the original document to the firstroller; and a driving unit configured to drive the second roller; areading unit configured to optically read the original document conveyedby the document conveying unit; an image forming unit configured to forman image on a sheet on the basis of image data read by the reading unit;and a controller configured to control the driving unit to therebytemporarily stop the conveyance of the original document in order toperform the detection by the first detecting unit in a state in which anend of the original document on a downstream side in the conveyingdirection of the original document is located further on the upstreamside in the conveying direction of the original document than a nipposition of the first roller.
 11. The apparatus according to claim 10,wherein the document conveying unit further includes a second detectingunit located between the second roller and the first detecting unit andconfigured to detect entrance of the original document, and thecontroller starts, when the second detecting unit detects the entranceof the original document, control for stopping the original document ina position of the detection by the first detecting unit.
 12. Theapparatus according to claim 11, wherein the driving unit includes: apulse motor; and a driver for the pulse motor, and the controller stars,when the second detecting unit detects the entrance of the originaldocument, counting of a number of pulses output to the driver and stopsthe original document in the position of the detection by the firstdetecting unit on the basis of a result of the counting.
 13. Theapparatus according to claim 10, wherein the first detecting unit is anon-contact detecting unit.
 14. The apparatus according to claim 13,wherein the first detecting unit includes: an ultrasound generating unitconfigured to generate ultrasound; and an ultrasound receiving unitconfigured to receive the ultrasound generated by the ultrasoundgenerating unit, and the ultrasound generating unit and the ultrasoundreceiving unit are opposed to each other across a conveying path for theoriginal document.
 15. The apparatus according to claim 14, wherein theultrasound generating unit is located further downstream in theconveying direction of the original document than the ultrasoundreceiving unit.
 16. The apparatus according to claim 11, wherein thesecond detecting unit is located below a conveying path for the originaldocument.
 17. The apparatus according to claim 10, wherein the documentconveying unit further includes a third roller configured to pick up theoriginal document to the second roller, and the second and third rollersare connected by a transmission mechanism.
 18. The apparatus accordingto claim 17, wherein the second roller is opposed to a fourth roller,the fourth roller inhibits double-feed of the original document pickedup by the third roller.
 19. A method of detecting double-feed of a sheetcomprising performing double-feed detection for the sheet in a state inwhich an end of the sheet on a downstream side in a conveying directionof the sheet is located further on an upstream side in the conveyingdirection of the sheet than a nip position of a roller configured tocorrect a tilt of the sheet.
 20. The method according to claim 19,wherein the double-feed detection is performed by a non-contact sensor.